Letters which will go on sale at Sotheby's reveal how artist Lucian Freud had a relationship with poet Stephen Spender during his teenage years.

The collection, which features 10 letters from Freud to Spender, has a total estimate of £42 000 and will be included in Sotheby's Contemporary Art Day auction on 2nd July.

The letters have come from the Spender family estate after having been in the family for 70 years. Also on sale from the family's estate is The Head of Gerda Boehm, 1961, by Frank Auerbach which has an estimate of £350 000.

Lucian Freud Letter to Stephen Spender, 1940Image via Sotheby's

Freud and Spender were in correspondence between 1939-1942 whilst the artist was studying as Cedric Morris' student at East Anglian School of Painting and Drawing, Essex.

Sotheby's senior international specialist in contemporary art, Oliver Barker commented: "More than just letters, they are artworks in their own right."

"Filled with drawings and watercolors, they show the workings of the artist, reflecting his artistic output at the time."

Freud, did have a reputation as a womaniser, having around 14 children by different women. Freud's appreciation for the male form is evident in perhaps one of his greatest nudes, his painting of Leigh Bowery, who died from Aids related illnesses in 1994.